Journal of Minerals & Materials Characterization & Engineering, Vol. 4, No.1, pp 31-46, 2005 Printed in the USA. All rights reserved
Figure 1: Single wall carbon nanotubes
Carbon Nanotube Based Composites- A Review
Rupesh Khare*, Suryasarathi Bose
Mumbai University Institute of Chemical Technology (UICT)
*author to whom all the correspondence should be addressed
Carbon nanofibers and nanotubes are promising to revolutionise several fields in
material science and are a major component of nanotechnology. Further market
development will depend on material availability at reasonable prices. Nanotubes have a
wide range of unexplored potential applications in various technological areas such as
aerospace, energy, automobile, medicine, or chemical industry, in which they can be
used as gas adsorbents, templates, actuators, composite reinforcements, catalyst
supports, probes, chemical sensors, nanopipes, nano-reactors etc. In this paper, recent
research on carbon nanotube composites are reviewed. The interfacial bonding
properties, mechanical performance, electrical percolation of nanotube/polymer and
ceramic are also reviewed.
Carbon nanotube
Elemental carbon in the sp
hybridization can form a variety
of amazing structures. Apart from
the well-known graphite, carbon
can build closed and open cages
with honeycomb atomic
arrangement. The first such
structure to be discovered was the
C60 molecule by Kroto
et al.
Although various carbon cages
were studied, it was only in 1991,
when Iijima
observed for the first
time tubular carbon structures. The
nanotubes consisted of up to
several tens of graphitic shells (so-
called multi-walled carbon
nanotubes (MWNT)) with
adjacent shell separation of 0.34
nm, diameters of 1 nm and high
length/diameter ratio. Two years later, Iijima and Ichihashi
and Bethune et al.
synthesized single-walled carbon nanotubes (SWNT) (figure1).
Rupesh Khare, Suryasarathi BoseVol. 4, No. 1
Figure 2: tip of multi wall carbon nanotube
Figure 3: Arc-discharge scheme. Two
graphite electrodes are used to produce a dc
electric arc-discharge in inert gas
There are two main types of
carbon nanotubes
that can have
high structural perfection. Single-
walled nanotubes (SWNT) consist
of a single graphite sheet seamlessly
wrapped into a cylindrical tube.
Multiwalled nanotubes (MWNT)
comprise an array of such nanotubes
that are concentrically nested like
rings of a tree trunk (figure 2).
Synthesis of CN
The MWNT were first discovered
in the soot of the arc-discharge method by
Iijima. This method had been used long before in the production of carbon fibers and
fullerenes. It took two more years for Iijima and Ichihashi
, and Bethune
et al. to
synthesize SWNT by use of metal catalysts in the arc-discharge method in 1993.
Significant progress was achieved by laser-ablation synthesis of bundles of aligned
SWNT with small diameter distribution by Smalley and co-workers
. Catalytic growth of
nanotubes by the chemical vapor decomposition (CVD) method was first used by
et al.
In 1991, Iijima reported the
preparation of a new type of finite
structures consisting of needle-like tubes
The tubes were produced using an arc-
discharge evaporation method similar to that
used for the fullerene synthesis. The carbon
needles, ranging from 4 to 30 nm in diameter
and up to 1 mm in length, were grown on the
negative end of the carbon electrode used for
the direct current (dc) arc-discharge
evaporation of carbon in an argon-filled
vessel (100 Torr) (see figure 3). Ebbesen and
reported large-scale synthesis of
MWNT by a variant of the standard arc-
discharge technique. Iijima used an arc-
discharge chamber filled with a gas mixture
of 10 Torr methane and 40 Torr argon. Two
vertical thin electrodes were installed in the center of the chamber. The lower electrode,
the cathode, had a shallow dip to hold a small piece of iron during the evaporation. The
arc-discharge was generated by running a dc current of 200 A at 20 V between the
Vo. 4, No 1. Carbon Nanotube Based Composites- A Review
Figure 4:Laser-ablation scheme: Laser beam vaporizes
target of a mixture of graphite and metal catalyst (Co, Ni)
in a horizontal tube in a flow of inert gas at controlled
pressure and in a tube furnace at 1200
C. The nanotubes
are deposited on a water-cooled collector outside the
electrodes. The use of the three components—argon, iron and methane, was critical for
the synthesis of SWNT. The nanotubes had diameters of 1 nm with a broad diameter
distribution between 0.7 and 1.65 nm. In the arc-discharge synthesis of nanotubes,
et al. used as anodes thin electrodes with bored holes, which were filled with a
mixture of pure powdered metals (Fe, Ni or Co) and graphite. The electrodes were
vaporized with a current of 95–105 A in 100–500 Torr of He. Large quantities of SWNT
were generated by the arc-technique by Journet
et al. The arc was generated between
two graphite electrodes in a reactor under helium atmosphere (660 mbar).
In 1996, Smalley and co-
workers produced high yields
(>70%) of SWNT by laser-
ablation (vaporization) of graphite
rods with small amounts
of Ni
and Co at 1200
C (see figure 4).
The tube grows until too many
catalyst atoms aggregate on the
end of the nanotube. The large
particles either detach or become
over-coated with sufficient carbon
to poison the catalysis. This allows
the tube to terminate with a
fullerene-like tip or with a catalyst
particle. Both arc-discharge and
laser-ablation techniques have the
advantage of high (>70%) yields of SWNT and the drawback that (1) they rely on
evaporation of carbon atoms from solid targets at temperatures >3000
C, and (2) the
nanotubes are tangled which makes difficult the purification and application of the
Chemical vapour deposition (CVD)
Despite the described progress of synthetic techniques
for nanotubes, there still
remained two major problems in their synthesis, i.e. large scale production and ordered
synthesis. But, in 1996 a CVD method emerged as a new candidate for nanotube
synthesis. This method is capable of controlling growth direction on a substrate and
a large quantity of nanotubes. In this process a mixture of hydrocarbon
gas, acetylene, methane or ethylene and nitrogen was introduced into the reaction
chamber. During the reaction, nanotubes were formed on the substrate by the
decomposition of the hydrocarbon at temperatures 700–900
C and atmospheric
The process has two main advantages: the nanotubes are obtained at much lower
Rupesh Khare, Suryasarathi BoseVol. 4, No. 1
Figure 5: CVD reactor
temperature, although this is at the cost of lower quality, and the catalyst can be deposited
on a substrate, which allows for the formation of novel structures.
The substrate
The preparation of the substrate and the use of the catalyst deserve special
attention, because they determine the structure of the tubes. The substrate is usually
silicon, but also, glass and alumina are used. The catalysts are metal nanoparticles, like
Fe, Co and Ni, which can be deposited on silicon substrates either from solution, electron
beam evaporation or by physical sputtering. The nanotube diameter depends on the
catalyst particle size, therefore, the catalyst deposition technique, in particular the ability
to control the particle size, is critical to develop nanodevices. Porous silicon is an ideal
substrate for growing self-oriented nanotubes on large surfaces. It has been proven that
nanotubes grow at a higher ratio (length per minute), and they are better aligned than on
plain silicon
. The nanotubes grow parallel to each other and perpendicular to the
substrate surface, because of catalyst–surface interaction and the van der Waals forces
developed between the tubes.
The sol–gel
The sol–gel method uses a dried silicon gel, which has undergone several
chemical processes, to grow highly aligned nanotubes. The substrate can be re-used after
depositing new catalyst particles on the surface. The length of the nanotube arrays
increases with the growth time, and reaches about 2mm after 48-h growth
Gas phase metal catalyst
In the methods described
above, the metal catalysts are
deposited or embedded on the
substrate before the deposition of the
carbon begins. A new method is to
use a gas phase for introducing the
catalyst, in which both the catalyst
and the hydrocarbon gas are fed into a
furnace, followed by catalytic
reaction in the gas phase. The latter method is suitable for large-scale synthesis, because
the nanotubes are free from catalytic supports and the reaction can be operated
continuously. A high-pressure carbon monoxide (CO) reaction method, in which CO gas
reacts with iron pentacarbonyl, Fe(CO)
to form SWNT, has been developed
have also been synthesized from a mixture of benzene and ferrocene, Fe(C
in a
hydrogen gas flow
. In both methods, catalyst nanoparticles are formed through thermal
decomposition of organo metallic compounds, such as iron pentacarbonyl and ferrocene.
Vo. 4, No 1. Carbon Nanotube Based Composites- A Review
The reverse micelle method is promising, which contains catalyst nanoparticles (Mo and
Co) with a relatively homogeneous size distribution in a solution. The presence of
surfactant makes the nanoparticles soluble in an organic solvent, such as toluene and
benzene. The colloidal solution can be sprayed into a furnace, at a temperature of
C; it vaporizes simultaneously with the injection and a reaction occurs to form a
carbon product. The toluene vapour and metal nanoparticles act as carbon source and
catalyst, respectively. The carbon product is removed from the hot zone of the furnace by
a gas stream (hydrogen) and collected at the bottom of the chamber
Recent trends in the synthesis of CNT
Kirsten Edgar and John L. Spencer
synthesized carbon nanotubes from an
aerosol precursor. Solutions of transition metal cluster compounds were atomized by
electro hydrodynamic means and the resultant aerosol was reacted with ethyne in the gas
phase to catalyse the formation of carbon nanotubes. The use of an aerosol of iron
pentacarbonyl resulted in the formation of multi-walled nanotubes, mostly 6–9 nm in
diameter, whereas the use of iron dodecacarbonyl gave results that were concentration
dependent. High concentrations resulted in a wide diameter range (30–200 nm) whereas
lower concentrations gave multi-walled nanotubes with diameters of 19–23 nm.
Luciano Andrey Montoro et al synthesized
SWNT by arc water process. They
could synthesize high-quality SWNT and MWNT through arc-discharge in H
aqueous solution from pure graphite electrodes. They suggested that the VO group acts as
a nucleation agent promoting the growth of this more ordered carbon structure. The
compound was used to avoid the presence of metallic cations, and it was obtained
from a reaction commonly used for the synthesis of xerogels
et al. prepared
CNT by electrically arcing carbon rods in helium
(99.99%) in a stainless steel chamber with an inner diameter of 600 mm and a height of
350 mm. The anode was a coal-derived carbon rod (10 mm in diameter, 100–200 mm in
length); the cathode was a high-purity graphite electrode (16 mm in diameter, 30 mm in
length). The helium gas functioned as buffer gas and its pressure was varied in range of
0.033–0.076 MPa in the experiment. The voltage and current for arcing were controlled
at 30–40 V and 50–70 A, respectively.
Mingwang Shao
et al. synthesized CNT via a novel route using an iron catalyst
at the extremely low temperature of 180
C. In this process, carbon sub oxide was used as
carbon source, which changed to freshly formed free carbon clusters through
disproportionation. The carbon clusters can grow into nanotubes in the presence of Fe
catalyst, which was obtained by the decomposition of iron carbonyl Fe
at 250
under nitrogen atmosphere.
SWNT have been successfully synthesized using a fluidized-bed method
involves fluidization of a catalyst/support at high temperatures by a hydrocarbon flow,
Rupesh Khare, Suryasarathi BoseVol. 4, No. 1
shows promise for the large-scale, potentially
continuous, production of SWNT, at high
A new method, which combines non-equilibrium plasma reaction
with template-
controlled growth technology, has been developed for synthesizing aligned carbon
nanotubes at atmospheric pressure and low temperature. Multiwall carbon nanotubes with
diameters of approximately 40 nm were restrictedly synthesized in the channels of anodic
aluminum oxide template from a methane hydrogen mixture gas by a.c. corona discharge
plasma reaction at a temperature below 200
In a recent technique, Nebulized spray pyrolysis
, large-scale synthesis of
MWNT and aligned MWNT bundles is reported. Nebulized spray is a spray generated by
an ultrasonic atomizer. MWNT with fairly uniform diameters as well as aligned MWNT
bundles have been obtained by using solutions of organometallic compounds such as
ferrocene in benzene, toluene and other hydrocarbon solvents. A SEM image of aligned
MWNT bundles obtained by the pyrolysis of a nebulized spray of ferrocene–toluene–
acetylene mixture .The advantage of using a nebulized spray is the ease of scaling into an
industrial scale process, as the reactants are fed into the furnace continuously (figure 6).
Properties of CNT
Electrical properties
The Unique Electrical Properties of carbon nanotubes are to a large extent
from their 1-D character and the peculiar electronic structure of graphite. They
have extremely low electrical resistance. Resistance occurs when an electron collides
with some defect in the crystal structure of the material through which it is passing. The
defect could be an impurity atom, a defect in the crystal structure, or an atom vibrating
Figure 6: Schematic representation of Nebulized spray
pyrolysis technique for synthesis of CNT
Vo. 4, No 1. Carbon Nanotube Based Composites- A Review
about its position in the crystal. Such collisions deflect the electron from its path. But the
electrons inside a carbon nanotube are not so easily scattered. Because of their very small
diameter and huge ratio of length to diameter—a ratio that can be up in the millions or
even higher. In a 3-D conductor, electrons have plenty of opportunity to scatter, since
they can do so at any angle. Any scattering gives rise to electrical resistance. In a 1-D
conductor, however, electrons can travel only forward or backward. Under these
circumstances, only backscattering (the change in electron motion from forward to
backward) can lead to electrical resistance. But backscattering requires very strong
collisions and is thus less likely to happen. So the electrons have fewer possibilities to
scatter. This reduced scattering gives carbon nanotubes their very low resistance. In
addition, they can carry the highest
current density of any known material, measured
as high as 10
. One use for nanotubes that has already been developed is as
extremely fine electron guns, which could be used as miniature cathode ray tubes (CRTs)
in thin high-brightness low-energy low-weight displays. This type of display would
consist of a group of many tiny CRTs, each providing the electrons to hit the phosphor of
one pixel, instead of having one giant CRT whose electrons are aimed using electric and
magnetic fields. These displays are known as Field Emission Displays (FEDs). A
nanotube formed by joining nanotubes of two different diameters end to end can act as a
diode, suggesting the possibility of constructing electronic computer circuits entirely out
of nanotubes. Nanotubes have been shown to be superconducting at low temperatures.
Mechanical properties
The carbon nanotubes are expected to have high stiffness and axial strength as a
result of the carbon–carbon sp
. The practical application of the nanotubes
requires the study of the elastic response, the inelastic behavior and buckling, yield
strength and fracture. Efforts have been applied to the experimental
and theoretical
investigation of these properties. Nanotubes are the stiffest known fiber, with a measured
Young's modulus
of 1.4 TPa. They have an expected elongation to failure of 20-30%,
which combined with the stiffness, projects to a tensile strength well above 100 GPa
(possibly higher), by far the highest known. For comparison, the Young's modulus
high-strength steel is around 200 GPa, and its tensile strength is 1-2 GPa.
Thermal Properties
Prior to CNT, diamond was the best thermal conductor. CNT have now been
shown to have a thermal conductivity at least twice that of diamond
. CNT have the
unique property of feeling cold to the touch, like metal, on the sides with the tube ends
exposed, but similar to wood on the other sides. The specific heat and thermal
conductivity of carbon nanotube systems are determined primarily by phonons. The
measurements yield linear specific heat and thermal conductivity above 1 K and below
room temperature
while a T
behavior of the specific heat was observed below 1 K.
The linear temperature dependence can be explained with the linear k-vector dependence
of the frequency of the longitudinal and twist acoustic phonons
. The specific behavior
Rupesh Khare, Suryasarathi BoseVol. 4, No. 1
of the specific heat below 1 K can be attributed to the transverse acoustic phonons with
quadratic k dependence
. The measurements of the thermoelectric power (TEP) of
nanotube systems give direct information for the type of carriers and conductivity
Polymer matrix composite
Since the documented discovery of carbon nanotubes (CNT) in 1991 by Iijima
and the realization of their unique
physical properties, including mechanical, thermal,
and electrical, many investigators have endeavored to fabricate advanced CNT composite
materials that exhibit one or more of these properties. For example, as conductive filler in
polymers, CNT are quite effective compared to traditional carbon black microparticles,
primarily due to their high aspect ratios. The electrical percolation threshold was recently
reported at 0.0025 wt. % CNT and conductivity at 2 S/m at 1.0 wt% CNT in epoxy
(figure 7).
Similarly, CNT possess one of the highest thermal conductivities known
, which
suggests their use in composites for thermal management. The CNT can be thought of as
the ultimate carbon fiber with break strengths reported as high as 200 GPa, and elastic
moduli in the 1TPa range
. This, coupled with approximately 500 times more surface
area per gram (based on equivalent volume fraction of typical carbon fiber) and aspect
ratios of around 103, has spurred a great deal of interest in using CNT as a reinforcing
phase for polymer matrices. Increasing attention is being focused on the CNT surface,
Figure 7: Semi- log plot
of the specific composite conductivity as a function of
carbon nanotube weight fraction p: The insert shows a log–log plot of the
conductivity as a function of p – p
with an exponent t of 1.2
Vo. 4, No 1. Carbon Nanotube Based Composites- A Review
namely the interface between the CNT and surrounding polymer matrix. From micro-
mechanics, it is through shear stress build-up at this interface that stress is transferred
from the matrix to the CNT. Numerous researchers have attributed lower-than-predicted
CNT-polymer composite properties to a lack of interfacial bonding
56, 57
. If one considers
the surface of a CNT, essentially an exposed graphene sheet, it is not surprising that
interfacial interaction is a concern. It is the weak inter-planar interaction of graphite that
provides its solid lubricant quality, and resistance to matrix adhesion. This is exaggerated
by the chemically inert nature of graphene structures. Significant toughening of polymer
matrices through the incorporation of CNT has been reported
. A loading of 1 wt%
MWNT, randomly distributed in an ultra-high molecular weight polyethylene was
reported to increase the strain energy density by 150% and increase the ductility by
140%. Secondary crystallites, which nucleated from the MWNT, were attributed a
higher mobility and hence the increase in strain energy
. A similar effect was found in
aligned MWNT/polyacrylonitrile. Fibers containing 1.8 vol. % MWNT with an
approximately 80% increase in energy to yield and energy to break
. A process of
spinning 60 wt% SWNT/polyvinylalcohol fibers with pre-drawn energy absorbing
capacity nearly 3.5 times spider silk (165 J/g) was reported
. Slippage between SWNT
bundles was suggested as the mechanism responsible for the enhancement in the
toughness. The addition of 1 wt% MWNT to isotactic polypropylene (iPP) was shown to
affect crystal nucleation from differential scanning calorimetry and X-ray diffraction
. Compared with neat iPP, there was an increase in crystallization rate for
the composite material with evidence of fibrillar crystal growth rather than spherulite
growth. These modifications in the morphology of a polymer matrix combined with the
energy required for CNT debonding and pull-out suggest CNT may augment the energy
absorption or toughness characteristics of the composite. A twofold increase in the
tension–tension fatigue strength for an aligned SWNT/epoxy composite was found in
comparison to typical carbon fiber/epoxy composites. Embedded CNT
may effectively
prolong the formation of and/or bridge micro cracking/ crazing that can propagate and
lead to fatigue failure. CNT reinforced polymer composites are seen as a potentially
fruitful area for new, tougher or fatigue resistant materials. Further investigations into the
toughness and fatigue properties of these composites are needed to understand the
reinforcing mechanism at work.
The influence of carbon nanotube (CNT) contents on electrical and rheological
properties of CNT-reinforced polypropylene (PP) composites was studied. As a result,
the volume resistivity of the composites was decreased with
increasing the CNT content
and the electrical percolation threshold was formed between 1 and 2 wt% CNT, which
were caused by the formation of conductive chains in the composites (figure 8). And the
viscosity of the composites was increased with the addition of CNT, which was
accompanied by an increase in elastic melt properties (figure 9). This could be explained
by the higher aspect ratio of the CNT. And the composites containing more than 2 wt%
CNT exhibited non-Newtonian curves at low frequency.
Polyimide/carbon nanotube (PI/CNT) nanocomposites
with different
proportions of CNT were fabricated by in situ process. The bending strength and
microhardness of the PI/CNT nanocomposites were measured. The friction and wear
Rupesh Khare, Suryasarathi BoseVol. 4, No. 1
behavior of the nanocomposites
was evaluated on an M-2000
friction and wear tester. The
results showed that the bending
strength and microhardness of
the PI/CNT nanocomposites
increased with increasing CNT
content and reached stable
values at a certain content of
CNT. CNT could effectively
enhance the friction-reduction
and antiwear capacity of the
nanocomposite because it
increased the load capacity and
mechanical strength of the
CNT/PI. The variables such as
applied load and sliding speed
had a significant influence on
friction and wear performance.
Composites of high molecular
weight polyaniline (PANI)
various weight percentages of single-
walled carbon nanotubes (SWNT)
were fabricated using solution
processing. Electrical characteristics
of metal–semiconductor (MS) devices
fabricated from the PANI/SWNT
composites were studied. Current–
voltage (I–V) characteristics of these
devices indicate a significant increase
in current with an increase in carbon
nanotube concentration in the
Emilie et al.
found that the tensile modulus and yield strength increased with the
addition of SWNT loading in a polyimide SWNT composite. The increase was much
higher than that observed for film samples (which were cast without preferred SWCNT
orientation), but much less than what was expected from an oriented discontinuous fiber
reinforced polymer composite. This low level of improvement was likely due to
inefficient and incomplete dispersion. With the aid of improved dispersion, significant
reinforcing effects of the aligned fibers on the mechanical properties are anticipated.
Improvements in mechanical reinforcement may also be realized with a matrix designed
to promote uniform dispersion by capitalizing on physical interaction with SWCNT
inclusions to improve the nanotube/matrix interface so as to maximize load transfer
across the interface.
Figure 8: Electrical volume resistivity
composites as a function of
nanotube content.
Content of MWNT (wt%)
Figure 9: Viscosity of MWNT/PP composites
measured at 170
Vo. 4, No 1. Carbon Nanotube Based Composites- A Review
In a study by Pötschke
et al. a masterbatch of PC–
(15 wt%) was diluted
with different amounts of PC in
a small scale conical twin
screw extruder (DACA Micro
Compounder) to obtain
different compositions of
MWNT. In this system,
electrical measurements
indicated percolation of
MWNT between 1.0 and 1.5 wt
%( figure10).
A novel
polyacrylamide–carbon nanotubes
(PAM–CNT) copolymer has been prepared by
ultraviolet radiation initiated polymerization. The PAM–CNT copolymer was
characterized by the instruments of Fourier transform infrared spectroscopy, UV–vis
absorbance spectra, fluorescence spectra and transmission electron microscope. The
morphology and microtribological properties of PAM–CNT thin films on mica were
investigated by atomic force microscopy/friction force microscopy (AFM/FFM). The
friction of the films was stable with the change of applied load and the friction coefficient
decreased significantly as the CNT addition. The results show that the rigid rod-like CNT
in polymer would enhance load-bearing and anti-wear properties of the thin films.
SMA encapsulated
are melt mixed with
PA12 matrix in a conical twin-
screw extruder. The process of
encapsulation by SMA
copolymer leads to a finer
dispersion of SWNT and
enhanced interfacial adhesion
between PA12 and SMA
modified SWNT. This leads to
enhanced mechanical
properties, which is
manifested by tensile and
dynamic mechanical
properties. Formation of
network structure (figure 11)
has been identified in
unmodified SWNT composites
by electrical conductivity measurements and morphological investigations by scanning
electron microscopy.
Figure 10: Electrical conductivity
vs. MWNT
contents for PC– MWNT composites.
Figure 11: SEM of the composite
PA12+6 wt% SWNT after
tensile testing, area near fracture surface.
Rupesh Khare, Suryasarathi BoseVol. 4, No. 1
Zou et al. showed that for the dispersion of MWNT in a polymer
matrix by
screw extruder, there is a critical MWNT concentration of 1.0 wt% where a fine network
of filler is formed; therefore the composites possess improved mechanical properties.
Shuying et al. found from DSC analysis that the introduction of SWNT
increases the glass transition temperature of the composites and low concentration of
SWNT act as nucleating agents to the crystallization of ABS as small melting peaks were
observed at 0.5 wt% and 1 wt% of SWNT.
improvements in the
of the
nanocomposites were
illustrated by a 50.8%
increase in the storage
modulus by Liao et al.
(figure 12).
The significant
improvements of
nanotube dispersion
and mechanical
performance were
attributed to the
combined use of tip
sonication and acetone
as dispersion aids during sample processing.
Nanocomposites consisting of double-wall carbon nanotubes
(DWCNT) and an
epoxy matrix were produced by a standard calandering technique. A very good dispersion
of both DWCNT and carbon black (CB) in an epoxy resin could be observed. The
investigation of the (fracture-) mechanical properties resulted in an increase of strength,
Young’s modulus and strain to failure at a nanotube content of only 0.1 wt%. The
correlation of the experimentally obtained Young’s moduli showed a good agreement
with a modified Halpin-Tsai theory.
Poly (methyl methacrylate) (PMMA) nanocomposites have been processed
melt blending. The amount of nano fibers used was 5 and 10 wt%, respectively. The
PMMA/CNF composites were processed into 4 mm diameter rods and 60 mm diameter
fibers using small-scale melt spinning equipment. At 5 wt% CNF, composite rods as well
as fibers show over 50% improvement in axial tensile modulus as compared to the
control PMMA rod and fibers, respectively. The reinforcement efficiency decreased at 10
wt% CNF. The PMMA/CNF nanocomposites fibers also show enhanced thermal
Figure 12: Storage modulus of the nanocomposites
Vo. 4, No 1. Carbon Nanotube Based Composites- A Review
stability, significantly reduced shrinkage and enhanced modulus retention with
temperature, as well as improved compressive strength.
Polystyrene nanocomposites
with functionalized single-walled carbon nanotubes
(SWNT), prepared by the in-situ generation and reaction of organic diazonium
compounds, were characterized using melt-state linear dynamic viscoelastic
measurements. These were contrasted to the properties of polystyrene composites
prepared with unfunctionalized SWNT at similar loadings. The functionalized
nanocomposites demonstrated a percolated SWNT network structure at concentrations of
1 vol % SWNT, while the unfunctionalized SWNT-based composites at twice the loading
of SWNT exhibited viscoelastic behavior comparable to that of the unfilled polymer.
This formation of the SWNT network structure for the functionalized SWNT-based
composites is because of the improved compatibility between the SWNT and the polymer
matrix and the resulting better dispersion of the SWNT.
Ceramic matrix
Several experiments have recently confirmed
the theoretically predicted
outstanding mechanical properties of carbon nanotubes (CNT). Consequently, CNT
emerge as potentially attractive materials as reinforcing elements in ceramic matrix
composites. Massive CNT –Fe-Al
composites have been prepared by hot pressing.
Observations show that the CNT bundles remain present in the composites, but in a
smaller quantity than in the starting powder. The improvement of the composite
microstructure, the change in the nature of the matrix and attempts to align the CNT are
works actually in progress. CNT-ceramic composites become attractive materials
only for their enhanced mechanical properties, but also for the possibility to tailor the
electrical conductivity through the CNT content. A family of SWNT-MgAl
composites has been prepared, in a wide range of composition (0.23–24.5 vol% CNT)
and with a very homogeneous distribution of the SWNT between the matrix grains owing
to the in situ CCVD synthesis route. A jump of the DC electrical conductivity has been
measured. Up to 11 vol% CNT, the electrical conductivity is well fitted by the scaling
law of the percolation theory. CNT–metal-oxide composites
have been extruded at high
temperatures. For temperatures up to 1500 C, some of the CNT remain undamaged
neither by the high temperature nor by the extreme shear stresses. Moreover, the
superplastic forming is made easier by the CNTs, which inhibit the matrix grain growth
and also acts as a lubricating agent. It has been shown for the first time that it is possible
to align CNTs in ceramic-matrix nanocomposites. CNT–Fe–Al
composites have
been prepared by hot-pressing composite powders where the quantity of CNT has greatly
been increased in comparison with previous research.
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